The present invention relates to synchronizing means and methods therefor, and more particularly to means and methods for phase synchronizing the rotary motion of two or more rotating devices. For purposes of illustration, the invention will be discussed in connection with the phase synchronization of the operation of a receiving facsimile system with the operation of a transmitting facsimile system, but the invention has application for phase synchronizing rotating devices in general.
A facsimile system enables the electronic transmission of graphic or text information between a transmitting facsimile unit and a receiving facsimile unit. The facsimile receiving unit is usually located at a location remote from the facsimile transmitting unit. It is necessary for the receiving unit to be synchronized with the transmitting unit so that the print out transducers of the receiving unit will mark the same place in the copy material that the read transducers are scanning on the original document.
Many facsimile systems employ a synchronous motor. One well known method for attaining phase orientation of the synchronous motor output shaft with some reference rotation includes the steps of first sampling and comparing the phase orientation of the synchronous motor and the reference rotation, then blanking the electrical input signal to the synchronous motor to cause this rotor to slip one pole on the stator, i.e. to drop back at the time when the normal ac signal to the motor is blank. A disadvantage to this comparison and pole slipping procedure is that it has no more resolution than the number of poles set up on the standing field of the synchronous motor stator.
Another method proposed in the past has been to run the receiving facsimile motor at a speed different than the transmitting facsimile system and then to detect simultaneous occurrence of a mark generated by the receiving unit with a synchronizing mark sent by the transmitting unit. When coincidence of the two marks is detected, then the receiving unit is run at a speed synchronous with the transmitting unit. This assures proper synchronization and framing between the transmitting and receiving unit. However, one of the disadvantages of this type of a system is that the coincidence of the marks is only sensed or detected at one particular position of the rotation of the receiving unit. Normally, the receiver mark is generated by a sensor that is fixed in position with respect to a rotating shaft. The sensor generates a mark whenever a particular portion of the shaft goes past it. Although that particular portion of the shaft may be in synchronism with the transmitting mark at any angle or position of the shaft other than where the sensor is located the receiver will not be commanded to operate in synchronous speed because there is no way of detecting or determining when synchronism occurs other than when that particular angular portion of the shaft is in alignment with the sensor, which must occur at the same time that the transmitted mark is received. It will therefore be appreciated that such a method of synchronizing the two systems could be lengthy and time consuming.
In view of the foregoing, it should now be understood that it would be desirable to provide an improved facsimile synchronizing and framing system that would solve the above and other problems.
Accordingly, one of the objects of the present invention is to provide a method of synchronizing a facsimile system by using an up-down counter to generate a count that is proportional to position difference between the facsimile transmitter and receiver.
Another object of the invention is to provide an improved facsimile system wherein the transmitter and receiver are both synchronized to be in identical parts of the sweep at the same time without the requirement that this be done at only a predetermined angular position of a rotating shaft in the receiver.
Another object of the invention is to provide a system that synchronizes a receiver and transmitter facsimile systems in a minimum amount of time.
Yet another object of the present invention is to provide a facsimile system that employs an up-down counter to achieve proper framing synchronization.
A further object of the present invention is to provide a facsimile system which can operate independently from a frequency standard or speed reference that is precisely predetermined, so long as the facsimile transmitter and receiver are operating at the same frequency.